Closed-loop control algorithm for an eddy current braking system

Abstract

A method and system for controlling an eddy current braking system in a motor vehicle is provided. The motor vehicle includes a prime mover linked to the eddy current braking system to provide torque thereto, and the eddy current braking system has a retarder assembly including at least a rotor and a stator. The method includes the steps of detecting a feedback current from the retarder assembly, detecting a rotor speed of the rotor, providing a signal indicative of a desired retarding torque, and determining a command current for the retarder as a function of the feedback current, rotor speed and desired retarding torque using a closed-loop sliding-mode control algorithm. The command current is provided to the retarder to control application of torque to the prime mover.

What is claimed is:  
     
       1. A method for controlling an eddy current braking system in a motor vehicle, said motor vehicle having a prime mover linked to said eddy current braking system to provide torque thereto, and said eddy current braking system having a retarder assembly including at least a rotor and a stator, said method comprising the steps of: 
       detecting a feedback current from said retarder assembly;  
       detecting a rotor speed of said rotor;  
       providing a signal indicative of a desired retarding torque;  
       determining a command current for said retarder as a function of said feedback current, rotor speed and desired retarding torque using a closed-loop sliding-mode control algorithm; and  
       providing said command current to said retarder to control application of torque to said prime mover.  
     
     
       2. The method of  claim 1  wherein said sliding-mode control algorithm further implements a pre-determined convergence rate of η within the boundary layer of thickness φ. 
     
     
       3. The method of  claim 2  wherein said algorithm further comprises:          I   cmd     =       L       (         f   1          (   ω   )       +     2          f   2          (   ω   )          i       )        R            [                 T   .     des     -       ω   .          (              f   0            ω       +              f   1            ω          i     +              f   2            ω            i   2         )       +       (         f   1          (   ω   )       +     2          f   2          (   ω   )          i       )          R   L        i     +                            η                 SAT        {       1   φ          (       T   des     -     (         f   0          (   ω   )       +           f   1          (   ω   )       *        i     +           f   2          (   ω   )       *          i   2         )       )       }             ]                       
       wherein I cmd  is said command current, L is a coil winding inductance of said stator, R is a coil winding resistance of said stator, ω is said rotary speed, T des  is said desired retarding torque and i is said feedback current. 
     
     
       4. An eddy current braking system for a motor vehicle having a prime mover turning a shaft, said system comprising: 
       an eddy current brake including a rotor, a stator and a command current input, said rotor operably connected to said shaft;  
       at least one sensor operably connected to said rotor to detect a rotational speed of said rotor;  
       at least one sensor operably connected to said stator to determine a feedback current of said brake;  
       a computer in communication with said sensors;  
       a torque selector in communication with said computer for selecting a desired retarding torque; and  
       a memory accessible to said computer;  
       wherein said memory stores an algorithm for said computer to determine a command current I cmd  as a function of said feedback current, rotor speed and desired retarding torque.  
     
     
       5. The system of  claim 4  wherein said algorithm further comprises a closed-loop sliding-mode control algorithm. 
     
     
       6. The system of  claim 5  wherein said sliding-mode control algorithm further implements a pre-determined convergence rate of η within the boundary layer of thickness φ. 
     
     
       7. The system of  claim 6  wherein said algorithm further comprises:          I   cmd     =       L       (         f   1          (   ω   )       +     2          f   2          (   ω   )          i       )        R            [                 T   .     des     -       ω   .          (              f   0            ω       +              f   1            ω          i     +              f   2            ω            i   2         )       +       (         f   1          (   ω   )       +     2          f   2          (   ω   )          i       )          R   L        i     +                            η                 SAT        {       1   φ          (       T   des     -     (         f   0          (   ω   )       +           f   1          (   ω   )       *        i     +           f   2          (   ω   )       *          i   2         )       )       }             ]                       
       wherein I cmd  is said command current, L is a coil winding inductance of said stator, R is a coil winding resistance of said stator, φ is said rotary speed, T des  is said desired retarding torque and i is said feedback current. 
     
     
       8. The system of  claim 7  wherein the predetermined convergence rate within the boundary layer thickness further comprise values selected for maximum braking performance. 
     
     
       9. The control system of  claim 8 , further comprising a digital signal processor connected between the sensors and the computer, wherein the digital signal processor receives outputs from the sensors, processes the outputs, and sends the outputs to the computer. 
     
     
       10. A method for controlling an eddy current braking system in a motor vehicle, said motor vehicle having a prime mover linked to said eddy current braking system to provide torque thereto, and said eddy current braking system having a retarder assembly including at least a rotor and a stator, said method comprising the steps of: 
       providing rotor speed and feedback current information to a computer;  
       verifying that said rotor speed is above a minimum value;  
       calculating a command current as a function of said rotor speed, feedback current, and desired torque;  
       converting the command current into a pulse-width modulated signal; and  
       providing said signal to said eddy current brake stator.  
     
     
       11. The method of  claim 10  wherein said step of calculating a command current further comprises-applying said rotor speed, feedback current and desired torque to the following algorithm:          I   cmd     =       L       (         f   1          (   ω   )       +     2          f   2          (   ω   )          i       )        R            [                 T   .     des     -       ω   .          (              f   0            ω       +              f   1            ω          i     +              f   2            ω            i   2         )       +       (         f   1          (   ω   )       +     2          f   2          (   ω   )          i       )          R   L        i     +                            η                 SAT        {       1   φ          (       T   des     -     (         f   0          (   ω   )       +           f   1          (   ω   )       *        i     +           f   2          (   ω   )       *          i   2         )       )       }             ]                       
       wherein I cmd  is said command current, L is a coil winding inductance of said stator, η is a selected convergence rate, φ is a selected boundary layer thickness, R is a coil winding resistance of said stator, ω is said rotary speed, T des  is said desired retarding torque and i is said feedback current. 
     
     
       12. An eddy current braking system for a motor vehicle having a prime mover turning a shaft linked to said eddy current braking system to provide torque thereto, and said eddy current braking system having a retarder assembly including at least a rotor and a stator, said system comprising: 
       means for detecting a feedback current from said retarder assembly;  
       means for detecting a rotor speed of said rotor;  
       means for providing a signal indicative of a desired retarding torque;  
       means for determining a command current for said retarder as a function of said feedback current, rotor speed and desired retarding torque using a closed-loop sliding-mode control algorithm; and  
       means for providing said command current to said retarder to control application of torque to said prime mover.